1. Field of the Invention
This invention relates to an improved form of a semiconductor device package and to a process for making the package. More particularly, it relates to such a package in which a one-piece interconnection structure is used to provide a connection from the semiconductor device inside the package to the next level of packaging, such as a circuit board or module, and to a process for making the package including the one-piece interconnection structure.
2. Description of the Prior Art
In conventional packages for integrated circuits, the integrated circuit is sealed in a package with a lead frame extending from inside the package to form two lines of leads extending along opposing sides of the package. As originally developed, wire connections extend from contact pads on the integrated circuit to ends of the lead frame surrounding the integrated circuit and spaced from it. While automated wire bonding equipment was developed to attach these wire connections to the integrated circuit and to the lead frame, the wire bonding step became a production bottleneck, and a more efficient way to connect the integrated circuits to the lead frames was desired.
More recently, the so-called tape automated bonding (TAB) package and process has replaced wire bonded packages for many integrated circuits. In the TAB package and process, a metallic tape, which is thinner than the lead frame but similar in construction, is used to connect bonding pads on the integrated circuit to the ends of the lead frame inside the package. Unlike wire bonding, all of the connections between the integrated circuit and the tape are formed simultaneously in the TAB package and process. Both the lead frame and the metallic tape are formed in the required pattern of leads by spray etching planar strips of different thickness metal which have been masked to produce to desired patterns. While the TAB package and process represents a substantial improvement over the earlier wire bonding package and process, separate bonding steps are still required to attach the integrated circuit to the metallic tape (inner lead bond) and to attach the metallic tape to the lead frame (outer lead bond).
It has been recognized as desirable to provide a one-piece interconnection between the integrated circuit inside the package and the next level of packaging. Such a structure in the form of a package having leads formed from a single thickness of interconnection metal is disclosed, for example, in the first related application identified above. Attempts have been made to provide a tape structure having reduced lead thickness contact fingers for attaching to the integrated circuit by masking a metal strip of the thickness used for tapes on one side with a pattern for the desired interconnection and on the other side with a pattern which will allow the interconnection to be reduced in thickness near the ends which are to be bonded to the integrated circuit, in an effort to provide more flexibility in the contact fingers near their attachment to the integrated circuit. The so-masked structure is then spray etched from both sides. Such spray etching results in a structure in which the interconnection contact fingers near the ends to be attached to the integrated circuit have half the thickness of the remainder of the tape, since the etching from both sides breaks through at the middle of the thickness of the tape. Such a structure and process is disclosed, for example, in the second related application identified above. The structure and process as taught in this application is not suitable for approximating the physical characteristics of a two-piece lead frame-tape structure, because the starting lead frame thickness must meet existing standards for the type of package being fabricated. Specifying the thickness of the lead frame structure also defines the thickness of the reduced thickness fingers in the prior art structure and process, i.e., it is half the thickness of the rest of the structure, and the resulting structure docs not match the characteristics of the lead frame-tape structure.
In an interconnection structure, the contact fingers extend at different angles with respect to the opposing edges of the structure toward the interiorly located integrated circuit chip. During assembly operations, the interconnection structure is flexed, and these different extending angles result in distortion of the contact fingers. The second related application discloses the use of certain areas of reduced thickness in an effort to increase flexibility of an assembly tape, but the patterns so employed do not solve the problem of contact finger distortion.